The invention relates to an apparatus for sorting substantially flat objects, such as mail items and documents. Such apparatus are provided with two or more sorting holders for storing objects stackwise in a stacking direction, a conveying system for conveying objects with at least one switch and at least two branches of the conveying system that connect thereto downstream, a reading unit for reading information from objects to be sorted, a processor connected with the reading unit for processing signals received from that reading unit and connected with the switch for operating the switch, and feed means for transporting objects from at least one of the sorting holders to a portion of the conveying system upstream of the switch.
Sorting flat objects, such as mail items and documents, by means of such apparatus, generally comprises the following operations: reading information from objects to be sorted, determining for each object a sorting indication on the basis of the information read from the relevant object, a first sorting operation wherein for each object one of at least two sorting holders is selected depending on the sorting indication of the relevant object and the objects are each conveyed to the sorting holder selected therefor and stacked in the sorting holders in a stacking direction, always in a position transverse to the stacking direction, and at least one further sorting operation, wherein at least a number of the objects are taken out of the sorting holders again, a sorting holder is selected for each object again and the objects are each conveyed to the sorting holder selected therefor and stacked in the sorting holders in a stacking direction, always in a position transverse to the stacking direction.
Such an apparatus and such a method are known from U.S. Pat. No. 5,112,042. Further, the invention relates to modules for composing an apparatus according to a special embodiment of the invention.
In U.S. Pat. No. 5,009,321, a system is described wherein, for mechanically sorting relatively small numbers of objects over a relatively large number of sorting positions (for instance addresses), a sorting algorithm with several sorting operations is utilized. According to the example, mail items for an area of 400 addresses are sorted by sorting a batch of objects to be sorted twice in succession over 20 pockets. A drawback of this system is that after the first sorting operation, the objects should be removed from the sorting pockets and deposited into the system in the correct order by the operator.
U.S. Pat. No. 5,112,042, cited hereinabove, describes a sorting machine of which sorting holders are adapted to store objects stackwise. The sorting holders comprise slides and stops whereby the objects can be removed in clusters from the sorting holders. The slides are movable to and fro in stacking direction and can moreover be swivelled between a position in alignment with objects in the sorting holder and a position beside the objects stacked in the sorting holder. For again feeding clusters of objects removed from the sorting holders, this sorting machine comprises a recirculation holder or several recirculation holders. The or each recirculation holder is displaceable between a position in alignment with one of the sorting holders and a position in alignment with the feed path to the reading unit.
Drawbacks of this system are that the construction with slides, stops and a recirculation holder or several recirculation holders is complicated and costly, and that displacement of the clusters of objects involves a relatively great chance of problems, because as a rule, a stack of incoming mail is highly irregular, as a result of which objects can easily be "squeezed from the stacks".
According to U.S. Pat. No. 5,143,225, the problems inherent in displacing clusters of objects are overcome by providing an apparatus with sorting pockets in the form of double conveyor belts, where between the objects can be retained in the manner of roof tiles. The apparatus comprises a first set of these sorting pockets for carrying out a first sorting operation. During the second sorting operation, the objects are fed from the first set of sorting pockets and conveyed to a second set of sorting pockets. However, the construction of this apparatus is also complicated, costly and voluminous, in that it comprises a large number of sorting holders in the form of very long double belts.
U.S. Pat. No. 5,042,667 also describes an apparatus having a first set of holders and a second set of holders. The first set of holders is constructed as a circuitous conveyor with positions for all objects to be sorted. The second set of holders is constructed as a smaller number of pockets to which objects fed from the first set of holders can be moved. The objects in the first set of holders move along an output position. When an object for the output position is next in turn for being received in one of the holders of the second set, it is removed from the first set of holders and conveyed to the selected holder of the second set of holders. This apparatus is complicated, costly and voluminous as well, particularly because the first set of holders is constructed as a circuitous path with positions for all objects to be sorted.
European patent application 0 429 118 discloses a sorting system comprising buffer pockets for storing and delivering individual objects. The objects delivered are discharged so that they will not automatically be fed for passing through a second sorting operation. Moreover, this apparatus is of course also complicated, costly and voluminous, because of the holders that are each designed for temporarily storing one object, a very large number are required in order to obtain a more or less effective apparatus. There is described an embodiment having 12 buffers, each consisting of 64 holders, i.e. 768 holders in total.
Consequently, the drawback inherent in each of these apparatus having sorting holders that can be emptied mechanically is that these apparatus are highly complicated and costly and take up much space.